The present invention relates to an apparatus and a method for measuring a time interval between scale pulse signals received when a revolution sensor, such as a revolution angle sensor or a revolution speed sensor, detects a revolution of a predetermined angle.
As is well known, a revolution sensor to be used as a revolution angle sensor or a revolution speed sensor provides a pulser and a pickup. The pulser, a disk fixed to a rotating shaft of a rotary machine for detecting a revolution angle, rotates with the rotary shaft. The peripheral face of the pulser provides cogs or poles formed at predetermined angle spacings. The pickup, fixed adjacent to the peripheral face of the pulser, generates a voltage signal whenever a cog or pole of the pulser passes by. This voltage signal is shaped into a pulse signal, and thus a scale pulse signal is produced whenever the rotary machine rotates an angle corresponding to a formed angle between the cogs or poles.
In the fuel injection control of a diesel engine in which a supply of fuel from a fuel injection pump to a fuel injection valve is controlled by an electromagnetic valve; a revolution angle of the fuel injection pump is detected by a revolution angle sensor every 10.degree. for example, a spacing time of each scale pulse signal given by this detection is measured, and based on the spacing time thus measured, the width of a revolution angle corresponding to a set of injection quantity is converted to a time width. The converted time width causes the electromagnetic valve to supply fuel in a time-controlled manner. Any error, existing in the formed angle between the cogs or poles of the revolution angle sensor, would not allow a correct time interval corresponding to a unit revolution angle of 10.degree. to be obtained, and consequently, cause an error in the time control of the electromagnetic valve. Therefore, the cogs or poles should be formed to obtain exact predetermined angles. This need is not only for fuel injection control, but is commonly utilized in any control system using a time interval which corresponds to a unit revolution angle detected by a revolution angle sensor.
However, from the manufacture standpoint, it is hard to form the cogs or poles with completely the same angle between them. For this reason, in the prior art of measuring a time interval between each scale pulse signal, an error occurs in the measured timer interval due to an error in the formed angle between the cogs or poles.